Vesicle (liposome) formation is a natural result of the amphiphilic nature of certain molecules. Amphiphilic molecules are the ones which have both hydrophilic and hydrophobic portions in the same molecule. For molecules in which the cross sectional area of the hydrophilic region is slightly less or equal to hydrophobic part of the molecule then the formation of bilayers is favored as seen in case of many phospholipids. Liposomes are formed by folding of these bilayers of amphiphilic molecules. They may be formed as a single bilayer enclosing a single aqueous space or they may be composed of concentric bilayers with many aqueous spaces alternating with bilayers (multilamellar vesicles). Liposomes can be used to encapsulate both hydrophobic and hydrophilic materials. Hydrophobic payloads are typically partitioned within the bilayers, whereas hydrophilic payloads are typically trapped within the aqueous compartment. The advantages of using liposomes as carrier/encapsulation systems are that they are stable and can protect their payload from degradation. Thus, in summary, the liposomes have been shown to be useful in (i) solubilising of both lipophilic as well as hydrophilic active compounds, (ii) protection of these active ingredients by encapsulation, (iii) prolonging action by slow release of active compounds and (iv) delivering active compounds to the specific target tissue.
Vesicles obtained from phospholipids have been used for timed delivery of a wide variety of materials including cosmetics, nutrients and pharmaceuticals. For example, U.S. Pat. No. 4,016,100 (1977) discloses a method of producing pharmaceutical composition comprised of an aqueous suspension of active ingredient entrapped in a spherule of a phospholipid. U.S. Pat. No. 3,957,971 (1976) discloses moisturizing liposomes wherein a humectant is in aqueous space of the vesicle. In addition to phospholipids, non-ionic amphiphiles have also been used. For example, U.S. Pat. No. 4,772,471 (1988) discloses liposomal spherules from non-ionic lipids to encapsulate pharmaceutically or cosmetically active substances. Recently, cationic liposomes from alkyl ammonium fatty acid salts for encapsulating both hydrophilic and hydrophobic loads have been provided by U.S. Pat. No. 6,071,535 (2000).
The harmful effects of solar UV-radiation on skin are well known. The UV-B (290–320 nm) portion of solar spectrum is largely responsible for erythema (sunburn) and cancer. [M. M. Rieger, Cosmet. Toiletries, 102 (3), 91, (1987); L. Taylor, Skin Cancer Foundation J., 4, (90) (1986)].
Similarly, photodegradative effect of UV-radiation on human hair is well documented. Continuous exposure to sunrays lightens hair color and makes human hair rough, brittle and difficult to comb. UV rays are reported to damage the proteins of cuticles. Prolonged irradiation results in diminished tensile strength due to breaking of disulphide bonds in keratin. [R. Beyak et al, J. Soc. Cosmet. Chem. 22, 667–668 (1971), E. Hoting et al, J. Soc. Cosmet. Chem. 46, 85–99 (1995)].
It is fairly established that the quaternary ammonium type of UV-absorbers are more substantive to both hair and skin than their non-quaternised counterparts. This superior substantivity is the result of interaction of cationic centres with the keratin of skin and hair. There are number of reports in literature describing this aspect of quaternary UV-absorbing molecules. [Saettone, M. F.; Giannaccini, B.; Morganti, C.; Persi, A.; Cipriani, C. Int. J. Cosmet. Sci., 8(1), 9–25, (1986), U.S. Pat. No. 5,427,773 (1995), U.S. Pat. No. 5,601,811 (1997), U.S. Pat. No. 6,613,340 (2003)]